In the upper reaches of suburban La Canada Flintridge, where mountainsides rise sharply from the backyards of homes, authorities put pink ribbons on the mailboxes of residents who stayed behind so they would know where to search in the event of a catastrophe.

One person who didn’t leave was Delos Tucker, a retired geologist who has lived in the community since the homes were built in 1962.

The county’s extensive flood-control system was working, but many of the basins designed to catch debris-laden runoff from fire-scarred mountains were full and evacuations remained necessary, Farber said.

“The Los Angeles County Fire Department is anticipating that a significant mud flow and debris flow is likely today,” said Chief DeputyJohn Tripp, announcing that fire departments in a five-county region had been put on alert that urban search and rescue teams might be needed.

The arrival of the new storm system shut down Interstate 5 in the snowy Tehachapi Mountains north of Los Angeles for the second day in a row, interrupting travel on one of state’s major arteries.

The storm was expected to drop 2 inches to 4 inches of rain in the already drenched foothills and mountains, with potentially strong downpours and intense rain rates, said National Weather Service meteorologist Eric Boldt.

Rain was expected to taper off by night, followed by showers on Friday and a dry weekend.

The major area of concern has been foothill communities along the perimeter of the San Gabriel Mountains, where a summer wildfire denuded 250 square miles of steep slopes northeast of Los Angeles.

The number of homes under evacuation orders has grown to more than 1,200 since the beginning of the week. Estimates of compliance have ranged up to 75 percent in some jurisdictions but down to 40 percent elsewhere.

As an overnight lull gave way to more rain at midmorning, public works crews shoveled mud from yards, driveways and gutters along Ocean View Boulevard in La Canada Flintridge. The neighborhood was otherwise all but deserted, with newspaper and mail deliveries cut off.

Tucker acknowledged that with catch basins filled with mud, water and debris, things could become difficult. But he said he had seen regrowth in the fire-scarred hills and believed it would hold soil in place.

At one point he left to bring his wife back from a visit to their daughter and defied a deputy who threatened to arrest him if he returned to his house. The deputy didn’t follow through on the threat, and Tucker was not upset by the incident.

“They have to play it super safe,” he said. “Obviously there is danger of a major mudflow coming down from the canyon.”

Despite the statewide extent of the storms, the number of deaths remained low. Two people were killed by falling trees, and police in Newman were searching for the body of a man who tried to drive across a flooded road.

In San Jose, a man died after falling 30 feet from the side of a freeway after he got out of a car that spun out in the rain and then jumped out of the path of an out-of-control car.